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1.
A new hybrid coupled model(HCM) is presented in this study, which consists of an intermediate tropical Pacific Ocean model and a global atmospheric general circulation model. The ocean component is the intermediate ocean model(IOM)of the intermediate coupled model(ICM) used at the Institute of Oceanology, Chinese Academy of Sciences(IOCAS). The atmospheric component is ECHAM5, the fifth version of the Max Planck Institute for Meteorology atmospheric general circulation model. The HCM integrates its atmospheric and oceanic components by using an anomaly coupling strategy. A100-year simulation has been made with the HCM and its simulation skills are evaluated, including the interannual variability of SST over the tropical Pacific and the ENSO-related responses of the global atmosphere. The model shows irregular occurrence of ENSO events with a spectral range between two and five years. The amplitude and lifetime of ENSO events and the annual phase-locking of SST anomalies are also reproduced realistically. Despite the slightly stronger variance of SST anomalies over the central Pacific than observed in the HCM, the patterns of atmospheric anomalies related to ENSO,such as sea level pressure, temperature and precipitation, are in broad agreement with observations. Therefore, this model can not only simulate the ENSO variability, but also reproduce the global atmospheric variability associated with ENSO, thereby providing a useful modeling tool for ENSO studies. Further model applications of ENSO modulations by ocean–atmosphere processes, and of ENSO-related climate prediction, are also discussed.  相似文献   

2.
The responses of the climate system to increase of atmospheric carbon dioxide(CO_2)arestudied by using a new version of the Bureau of Meteorological Research Centre(BMRC)globalcoupled general circulation model(CGCM).Two simulations are run:one with atmospheric CO_2concentration held constant at 330 ppm,the other with a tripling of atmospheric CO_2(990 ppm).Results from the 41-year control coupled integration are applied to analyze the mean state,seasonal cycle and interannual variability in the model.Comparisons between the greenhouseexperiment and the control experiment then provide estimations of the influence of increased CO_2on climate changes and climate variability.Especially discussed is the question on whether theclimate changes concerned with CO_2 inerease will impact interannual variability in tropical Pacific,such as ENSO.  相似文献   

3.
Five sets of model sensitivity experiments are conducted to investigate the influence of tropical cyclone (TC) genesis location and atmospheric circulation on interannual variability of TC intensity in the western North Pacific (WNP). In each experiment, bogus TCs are placed at different initial locations, and simulations are conducted with identical initial and boundary conditions. In the first three experiments, the specified atmospheric and SST conditions represent the mean conditions of El Nio, La Nia, and neutral years. The other two experiments are conducted with the specified atmospheric conditions of El Nio and La Nia years but with SSTs exchanged. The model results suggest that TCs generated in the southeastern WNP incurred more favorable environmental conditions for development than TCs generated elsewhere. The different TC intensities between El Nio and La Nia years are caused by difference in TC genesis location and low-level vorticity (VOR). VOR plays a significant role in the intensities of TCs with the same genesis locations between El Nio and La Nia years.  相似文献   

4.
The intensity of summer precipitation interannual variability is strongest over the middle and lower reaches of the Yangtze River Valley(MLYRV). The variability is larger than 1.5 mm d–1 and up to 35%–40% of the climatological mean summer precipitation. The relationship between the interdecadal change in the intensity of summer precipitation and its interannual variability over this area is investigated, by analyzing five gauged and re-constructed precipitation datasets. The relationship is found to be very weak over the MLYRV, with a correlation coefficient of only approximately 0.10. The Pacific Decadal Oscillation influences the western North Pacific subtropical high, which is responsible for the interdecadal change in summer precipitation over the MLYRV. However, the precipitation interannual variability is closely related to the ENSO events in the preceding winter due to its impact on the meridional displacement of the East Asian westerly jet. Different physical mechanisms cause different interdecadal variation in the intensity of summer precipitation and its interannual variability, and thus result in a poor relationship.  相似文献   

5.
The interannual variability of autumn precipitation over South China and its relationship with atmospheric circulation and SST anomalies are examined using the autumn precipitation data of 160 stations in China and the NCEP-NCAR reanalysis dataset from 1951 to 2004. Results indicate a strong interannual variability of autumn precipitation over South China and its positive correlation with the autumn western Pacific subtropical high （WPSH）. In the flood years, the WPSH ridge line lies over the south of South China and the strengthened ridge over North Asia triggers cold air to move southward. Furthermore, there exists a significantly anomalous updraft and cyclone with the northward stream strengthened at 850 hPa and a positive anomaly center of meridional moisture transport strengthening the northward warm and humid water transport over South China. These display the reverse feature in drought years. The autumn precipitation interannual variability over South China correlates positively with SST in the western Pacific and North Pacific, whereas a negative correlation occurs in the South Indian Ocean in July. The time of the strongest lag-correlation coefficients between SST and autumn precipitation over South China is about two months, implying that the SST of the three ocean areas in July might be one of the predictors for autumn precipitation interannual variability over South China. Discussion about the linkage among July SSTs in the western Pacific, the autumn WPSH and autumn precipitation over South China suggests that SST anomalies might contribute to autumn precipitation through its close relation to the autumn WPSH.  相似文献   

6.
This study investigates the influence of interannual vegetation variability. Two sets of offline and online simulations were performed using the Community Earth System Model. The interannual Global LAnd Surface Satellite （GLASS） leaf area index （LAI） dataset from 1985 to 2000 and its associated climatological LAI were used to replace the default climatological LAI data in version 4 of the Community Land Model （CLM4）. The re- sults showed that on a global scale, canopy transpiration and evaporation, as well as total evapotranspiration in offline simulations were significantly positively corre- lated with LAI, whereas ground evaporation and ground temperature showed significant negative correlation with LAI. However, the correlations in online simulations were reduced markedly because of interactive feedbacks between albedo, changed climatic factors and atmospheric variability. In the offline simulations, the fluctuations of differences in interannual variability of evapotranspiration and ground temperature focused on vegetation growing regions and the magnitudes were smaller. Those in online simulations spread over more regions and the magnitudes were larger. These results highlight the influence of interannual vegetation variability, particularly in online simulations, an effect that deserves consideration and attention when investigating the uncertainty of climate change.  相似文献   

7.
Based on four sets of numerical simulations prescribed with atmospheric radiative forcing and sea surface temperature（SST） forcing in the Community Atmospheric Model version 3（CAM3）, the interannual and interdecadal variabilities of the Antarctic oscillation（AAO） during austral summer were studied. It was found that the interannual variability is mainly driven by SST forcing. On the other hand, atmospheric radiative forcing plays a major role in the interdecadal variability. A cooling trend was found in the high latitudes of the Southern Hemisphere（SH） when atmospheric radiative forcing was specified in the model. This cooling trend tended to enhance the temperature gradient between the mid and high latitudes in the SH, inducing a transition of the AAO from a negative to a positive phase on the interdecadal timescale. The cooling trend was also partly weakened by the SST forcing, leading to a better simulation compared with the purely atmospheric radiative forcing run. Therefore, SST forcing cannot be ignored, although it is not as important as atmospheric radiative forcing.  相似文献   

8.
On the basis of Zeng’s theoretical design, a coupled general circulation model (CGCM) is developed with its characteristics different from other CGCMs such as the unified vertical coordinates and subtraction of the standard stratification for both atmosphere and ocean, available energy consideration, and so on. The oceanic component is a free surface tropical Pacific Ocean GCM between 30oN and 30oS with horizontal grid spacing of 1o in latitude and 2o in longitude, and with 14 vertical layers. The atmospheric component it a global GCM with low-resolution of 4o in latitude and 5o in longitude, and two layers or equal man in the vertical between the surface and 200 hPa. The atmospheric GCM includes comprehensive physical processes. The coupled model is subjected to seasonally-varying cycle. Several coupling experiments, ranging from straight forward coupling without flux correction to one with flux correction, and to so-called predictor-corrector monthly coupling (PCMC), are conducted to show the existence and final controlling of the climate drift in the coupled system. After removing the climate drift with the PCMC scheme, the coupled model is integrated for more than twenty years. The results show reasonable simulations of the annual mean and its seasonal cycle of the atmospheric and oceanic circulation. The model also produces the coherent interannual variations of the climate system, manifesting the observed El Ni?o / Southern Oscillation (ENSO).  相似文献   

9.
A regional Arctic Ocean configuration of the Massachusetts Institute of Technology General Circulation Model(MITgcm)is applied to simulate the Arctic sea ice from 1991 to 2012.The simulations are evaluated by comparing them with observations from different sources.The results show that MITgcm can reproduce the interannual and seasonal variability of the sea-ice extent,but underestimates the trend in sea-ice extent,especially in September.The ice concentration and thickness distributions are comparable to those from the observations,with most deviations within the observational uncertainties and less than 0.5 m,respectively.The simulated sea-ice extents are better correlated with observations in September,with a correlation coefficient of 0.95,than in March,with a correlation coefficient of 0.83.However,the distributions of sea-ice concentration are better simulated in March,with higher pattern correlation coefficients(0.98)than in September.When the model underestimates the atmospheric influence on the sea-ice evolution in March,deviations in the sea-ice concentration arise at the ice edges and are higher than those in September.In contrast,when the model underestimates the oceanic boundaries’influence on the September sea-ice evolution,disagreements in the distribution of the sea-ice concentration and its trend are found over most marginal seas in the Arctic Ocean.The uncertainties of the model,whereby it fails to incorporate the atmospheric information in March and oceanic information in September,contribute to varying model errors with the seasons.  相似文献   

10.
The grid-point atmospheric model of IAP LASG （GAMIL） was developed in and has been evaluated since early 2004. Although the model shows its ability in simulating the global climate, it suffers from some problems in simulating precipitation in the tropics. These biases seem to result mainly from the treatment of the subgrid scale convection, which is parameterized with Tiedtke＇s massflux scheme （or the Zhang-McFarlane scheme, as an option） in the model. In order to reduce the systematic biases, several modifications were made to the Tiedtke scheme used in GAMIL, including （1） an increase in lateral convective entrainment/detrainment rate for shallow convection, （2） inclusion of a relative humidity threshold for the triggering of deep convection, and （3） a reduced efficiency for the conversion of cloud water to rainwater in the convection scheme.
Two experiments, one with the original Tiedtke scheme used in GAMIL and the other with the modified scheme, were conducted to evaluate the performance of the modified scheme in this study. The results show that both the climatological mean state, such as precipitation, temperature and specific humidity, and interannual variability in the model simulation are improved with the use of this modified scheme. Results from several additional experiments show that the improvements in the model performance in different regions mainly result from either the introduction of the relative humidity threshold for triggering of the deep convection or the suppressed shallow convection due to enhanced lateral convective entrainment/detrainment rates.  相似文献   

11.
The interdecadal change in the interannual variability of the South China Sea summer monsoon(SCSSM) intensity and its mechanism are investigated in this study. The interannual variability of the low-level circulation of the SCSSM has experienced a significant interdecadal enhancement around the end of the 1980s, which may be attributed to the interdecadal changes in the evolution of the tropical Indo-Pacific sea surface temperature(SST) anomalies and their impacts on the SCSSM. From 1961 to 1989...  相似文献   

12.
A conceptual coupled ocean-atmosphere model was used to study coupled ensemble data assimilation schemes with a focus on the role of ocean-atmosphere interaction in the assimilation. The optimal scheme was the fully coupled data assimilation scheme that employs the coupled covariance matrix and assimilates observations in both the atmosphere and ocean. The assimilation of synoptic atmospheric variability that captures the temporal fluctuation of the weather noise was found to be critical for the estimation of not only the atmospheric, but also oceanic states. The synoptic atmosphere observation was especially important in the mid-latitude system, where oceanic variability is driven by weather noise. The assimilation of synoptic atmospheric variability in the coupled model improved the atmospheric variability in the analysis and the subsequent forecasts, reducing error in the surface forcing and, in turn, in the ocean state. Atmospheric observation was able to further improve the oceanic state estimation directly through the coupled covariance between the atmosphere and ocean states. Relative to the mid-latitude system, the tropical system was influenced more by ocean-atmosphere interaction and, thus, the assimilation of oceanic observation becomes more important for the estimation of the ocean and atmosphere.  相似文献   

13.
The response of the Pacific Decadal Oscillation （PDO） to global warming according to the Fast Ocean Atmosphere Model （FOAM） and global warming comparison experiments of 11 IPCC AR4 models is investigated. The results show that North Pacific ocean decadal variability, its dominant mode （i.e., PDO）, and atmospheric decadal variability, have become weaker under global warming, but with PDO shifting to a higher frequency. The SST decadal variability reduction maximum is shown to be in the subpolar North Pacific Ocean and western North Pacific （PDO center）. The atmospheric decadal variability reduction maximum is over the PDO center. It was also found that oceanic baroclinic Rossby waves play a key role in PDO dynamics, especially those in the subpolar ocean. As the frequency of ocean buoyancy increases under a warmer climate, oceanic baroclinic Rossby waves become faster, and the increase in their speed ratio in the high latitudes is much larger than in the low latitudes. The faster baroclinic Rossby waves can cause the PDO to shift to a higher frequency, and North Pacific decadal variability and PDO to become weaker.  相似文献   

14.
Using hindcasts of the Beijing Climate Center Climate System Model, the relationships between interannual variability （IAV） and intraseasonal variability （ISV） of the Asian-western Pacific summer monsoon are diagnosed. Predictions show reasonable skill with respect to some basic characteristics of the ISV and IAV of the western North Pacific summer monsoon （WNPSM） and the Indian summer monsoon （ISM）. However, the links between the seasonally averaged ISV （SAISV） and seasonal mean of ISM are overestimated by the model. This deficiency may be partially attributable to the overestimated frequency of long breaks and underestimated frequency of long active spells of ISV in normal ISM years, although the model is capable of capturing the impact of ISV on the seasonal mean by its shift in the probability of phases. Furthermore, the interannual relationships of seasonal mean, SAISV, and seasonally averaged long-wave variability （SALWV; i.e., the part with periods longer than the intraseasonal scale） of the WNPSM and ISM with SST and low-level circulation are examined. The observed seasonal mean, SAISV, and SALWV show similar correlation patterns with SST and atmospheric circulation, but with different details. However, the model presents these correlation distributions with unrealistically small differences among different scales, and it somewhat overestimates the teleconnection between monsoon and tropical central-eastern Pacific SST for the ISM, but underestimates it for the WNPSM, the latter of which is partially related to the too-rapid decrease in the impact of E1 Nifio-Southern Oscillation with forecast time in the model.  相似文献   

15.
The ability of AGCM to simulate the tropical intraseasonal oscillation (ISO) has been studied using the output of global spectral model (ALGCM (R42L9)) of the Institute of Atmospheric Physics, Chinese Academy of Sciences, and the outoput is compared with the results from NCEP/NCAR reanalysis for the year 1978-1989. The model displays an evident periodic signal of the tropical ISO. Basic propagating characters of the tropical ISO are captured, and changes in phase speed between Eastern and Western Hemispheres are also well presented, and the simulation of eastward propagation is better than that of westward propagation. This model has increased the ability to simulate the strength of the tropical ISO, especially at 200 hPa, and basically simulates the horizontal structure of wind characterized by the convergence in low-level and divergence in upper-level. The vertical structure of the zonal wind is also well reproduced. Moreover, observed results show that the representing of seasonal preference to form strong ISO in winter and spring is related to ISO's interannual variability, but it is shown in this model with strong ISO in winter and summer and weak ISO in spring and autumn. Structures of some physical elements such as vertical velocity, divergence, specific humidity, etc., and the special distribution of ISO have also differences with these from NCEP reanalysis data, which make it clear to develop this model to simulate the structure and spatial distribution of the ISO.  相似文献   

16.
The El Nin o-Southern Oscillation (ENSO) is modulated by many factors; most previous studies have emphasized the roles of wind stress and heat flux in the tropical Pacific. Freshwater flux (FWF) is another environmental forcing to the ocean; its effect and the related ocean salinity variability in the ENSO region have been of increased interest recently. Currently, accurate quantifications of the FWF roles in the climate remain challenging; the related observations and coupled ocean-atmosphere modeling involve large elements of uncertainty. In this study, we utilized satellite-based data to represent FWF-induced feedback in the tropical Pacific climate system; we then incorporated these data into a hybrid coupled ocean-atmosphere model (HCM) to quantify its effects on ENSO. A new mechanism was revealed by which interannual FWF forcing modulates ENSO in a significant way. As a direct forcing, FWF exerts a significant influence on the ocean through sea surface salinity (SSS) and buoyancy flux (Q B ) in the western-central tropical Pacific. The SSS perturbations directly induced by ENSO-related interannual FWF variability affect the stability and mixing in the upper ocean. At the same time, the ENSO-induced FWF has a compensating effect on heat flux, acting to reduce interannual Q B variability during ENSO cycles. These FWF-induced processes in the ocean tend to modulate the vertical mixing and entrainment in the upper ocean, enhancing cooling during La Nin a and enhancing warming during El Nin o, respectively. The interannual FWF forcing-induced positive feedback acts to enhance ENSO amplitude and lengthen its time scales in the tropical Pacific coupled climate system.  相似文献   

17.
Modeling the tropical Pacific Ocean using a regional coupled climate model   总被引：3，自引：0，他引：3  
A high-resolution tropical Pacific general circulation model (GCM) coupled to a global atmospheric GCM is described in this paper. The atmosphere component is the 5°×4°global general circulation model of the Institute of Atmospheric Physics (IAP) with 9 levels in the vertical direction. The ocean component with a horizontal resolution of 0.5°, is based on a low-resolution model (2°×1°in longitude-latitude).Simulations of the ocean component are first compared with its previous version. Results show that the enhanced ocean horizontal resolution allows an improved ocean state to be simulated; this involves (1) an apparent decrease in errors in the tropical Pacific cold tongue region, which exists in many ocean models,(2) more realistic large-scale flows, and (3) an improved ability to simulate the interannual variability and a reduced root mean square error (RMSE) in a long time integration. In coupling these component models, a monthly "linear-regression" method is employed to correct the model's exchanged flux between the sea and the atmosphere. A 100-year integration conducted with the coupled GCM (CGCM) shows the effectiveness of such a method in reducing climate drift. Results from years 70 to 100 are described.The model produces a reasonably realistic annual cycle of equatorial SST. The large SSTA is confined to the eastern equatorial Pacific with little propagation. Irregular warm and cold events alternate with a broad spectrum of periods between 24 and 50 months, which is very realistic. But the simulated variability is weaker than the observed and is also asymmetric in the sense of the amplitude of the warm and cold events.  相似文献   

18.
A coupled earth system model(ESM) has been developed at the Nanjing University of Information Science and Technology(NUIST) by using version 5.3 of the European Centre Hamburg Model(ECHAM), version 3.4 of the Nucleus for European Modelling of the Ocean(NEMO), and version 4.1 of the Los Alamos sea ice model(CICE). The model is referred to as NUIST ESM1(NESM1). Comprehensive and quantitative metrics are used to assess the model's major modes of climate variability most relevant to subseasonal-to-interannual climate prediction. The model's assessment is placed in a multi-model framework. The model yields a realistic annual mean and annual cycle of equatorial SST, and a reasonably realistic precipitation climatology, but has difficulty in capturing the spring–fall asymmetry and monsoon precipitation domains. The ENSO mode is reproduced well with respect to its spatial structure, power spectrum, phase locking to the annual cycle, and spatial structures of the central Pacific(CP)-ENSO and eastern Pacific(EP)-ENSO; however, the equatorial SST variability,biennial component of ENSO, and the amplitude of CP-ENSO are overestimated. The model captures realistic intraseasonal variability patterns, the vertical-zonal structures of the first two leading predictable modes of Madden–Julian Oscillation(MJO), and its eastward propagation; but the simulated MJO speed is significantly slower than observed. Compared with the T42 version, the high resolution version(T159) demonstrates improved simulation with respect to the climatology, interannual variance, monsoon–ENSO lead–lag correlation, spatial structures of the leading mode of the Asian–Australian monsoon rainfall variability, and the eastward propagation of the MJO.  相似文献   

19.
In this study,the NCEP/NCAR reanalysis dataset was used to analyze the variability modes of the winter upper-level wind field over Asian mid-high latitude region.As shown by the results,the dominant variability modes of the winter upper-level wind field over Asian mid-high latitude region are characterized by the out-of-phase variation in the intensity of the subtropical and temperate jets over East Asia and the meridional shift of the subtropical jet axis,on interannual and multiannual scales,respectively.The first leading variability mode can be used as a good measure to represent the integral variation of atmospheric general circulation in Asian mid-latitude region.Composite analyses suggest that the first leading variability mode of the winter upper-level wind field is intimately related to the atmospheric circulation and temperature anomalies in the northern hemispheric mid-latitude region.  相似文献   

20.
Weather and Climate Effects of the Tibetan Plateau   总被引：5，自引：1，他引：4  
Progress in observation experiments and studies concerning the effects of the Tibetan Plateau (TP) on weather and climate during the last 5 years are reviewed. The mesoscale topography over the TP plays an important role in generating and enhancing mesoscale disturbances. These disturbances increase the surface sensible heat (SH) flux over the TP and propagate eastward to enhance convection and precipitation in the valley of Yangtze River. Some new evidence from both observations and numerical simulations shows that the southwesterly flow, which lies on the southeastern flank of the TP, is highly correlated with the SH of the southeastern TP in seasonal and interannual variability. The mechanical and thermal forcing of the TP is an important climatic cause of the spring persistent rains over southeastern China. Moreover, the thermodynamic processes over the TP can influence the atmospheric circulation and climate over North America and Europe by stimulating the large-scale teleconnections such as the Asian-Pacific oscillation and can affect the atmospheric circulation over the southern Indian Ocean. Estimating the trend in the atmospheric heat source over the TP shows that, in contrast to the strong surface and troposphere warming, the SH over the TP has undergone a significant decreasing trend since the mid-1980s. Despite the fact that in situ latent heating presents a weak increasing trend, the springtime atmospheric heat source over the TP is losing its strength. This gives rise to reduced precipitation along the southern and eastern slopes of the TP and to increased rainfall over northeastern India and the Bay of Bengal.  相似文献   

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